Inoculating alloy for cast irons

ABSTRACT

The present invention relates to the sphere of alloys intended for improving cast iron, including the inoculation of grey or spheroidal cast irons with an alloy having the following composition: SILICON55 TO 85%CARBON 0.2 TO 1%CALCIUM 2 TO 5%ALUMINUMUP TO 2%THE REMAINDER BEING IRON WITH USUAL IMPURITIES.

United States Patent [191 Septier et al.

[111 3,765,875 [451 Oct.16, 1973 INOCULATING ALLOY FOR CAST IRONS 21 Appl. No.: 164,031

[30] Foreign Application Priority Data July 23, 1970 France 7027144 [52] US. Cl. 75/130 R, 75/134 S [51] Int. Cl. C22c 31/00, C22c 37/10 [58] Field of Search 75/58, 130, 130 R, 75/134 5,123 L [56] References Cited UNITED STATES PATENTS 2,139,515 12/1938 Norris 75/123 L 2,950,187 8/1960 Ototani 75/134 S 3,256,087 6/1966 Pfluger et al. 75/l34 S 3,323,899 6/1967 Forgeng et al. 75/O.5 BA 3,364,015 l/1968 Sump 75/134 S 2,705,196 3/1955 Wever et al. 75/58 3,301,663 l/l967 Wicher et a1, 75/58 3,304,174 2/1967 Ototani 75/58 X 3,575,695 4/1971 Miyashita et al. 75/58 X OTHER PUBLICATIONS Metals Hdbk, 8th Ed., Vol. 1, p. 392 & Vol. 5, P. 358, ASM, 1961.

Primary Examiner-L. Dewayne Rutledge Att0rneyMcDougall, Hersh & Scott ABSTRACT The present invention relates to the sphere of alloys intended for improving cast iron, including the inoculation of grey or spheroidal cast irons with an'alloy having the following composition:

silicon 55 to 85% carbon 0.2 to 1% -calcium 2 to 5% aluminum up to 2% the remainder being iron with usual impurities.

4 Claims, No Drawings INOCULATING ALLOY FOR CAST IRONS The present invention relates to alloys intended for improving cast iron.

The variation in mechanical characteristics, as a function of the chemical composition of a lamellar grey iron, is well known. The composition of the cast iron is generally expressed by its equivalent carbon and it is, for example, known that the tensile strength increases with decrease in carbon equivalent.

However, it is known that the reduction in equivalent carbon causes an increase in the tendency of the cast irons to solidify as a white structure. lnaddition, the use of cast irons having low equivalent carbon causes the presence of interdendritic graphite on the microstructure leading to poor characteristics in use.

On the other hand, it is known that an introduction, before casting, of silicon, in the form of an alloy or composite, known as inoculating agents," has a much more pronounced graphitizing effect than the silicon introduced in the same form into the charge of cast iron.

The use of such inoculants enables the precipitation of the white structure to be avoided and thus the use of cast irons of low equivalent carbon and high mechanical characteristics.

On the other hand, it is well known that the use of inoculating alloys is not limited to grey cast iron and that such alloys used on spheroidal graphite cast iron permit the improvement in such characteristics as:

lengthening of the time before disappearance of the previously introduced nodulizing effect,

refining of the grain,

improvement of the structure by elimination of carbides.

It is known that the ferro-silicons of different grades are among the inoculating alloys which are most frequently employed in the practice of inoculation.

The beneficial action of carbon, in the inoculation of cast irons, is also well known and its action, as compared with that of silicon, is indicated in Table l.

, TABLEl COMPARISON OF THE ACTION OF Si and C IN Table 1 shows that the carbon acts in the same manner as the silicon as regards the depth of temper, the structure and the hardness of the matrix, and that it is able to counter-balance the effect of enlargement of the graphitic structure produced bythe silicon.

It is well known that the ferro-silicons which are rich in silicon, even if they are manufactured in carburizing medium, contain little carbon. This is the case with industrial ferro-silicons which are generally employed for inoculating cast irons, so that it is not usually possible to take advantage of the beneficial action of the carbon for the inoculation. It has been proposed to make use of mixtures of ferrosilicon and graphite, but the use of this latter substance is not recommended when spheroidal graphite iron is prepared. ln addition, such mixtures do not permit a regular distribution of the additives to be obtained which is as fine as that which can be obtained by the use of homogeneous alloys.

1t is moreover known that calcium added to the ferrosilicon' exerts a reinforcing effect on the inoculation, similar to that of carbon.

The object of the invention is an inoculating alloy of a novel Fe-Si-Ca-C type, which is more effective than ferro-silicons to which carbon or calcium has been added.

It is an unexpectedly established fact that the effects of the carbon and calcium, introduced into the ferrosilicon, are mutually reinforced,,so that the gain obtained is better than the sum of the gains produced by the carbon and the calcium, when added individually.

The alloy of this invention contains 55 to 85 percent of silicon, 0.2 to 1 percent of carbon, 2 to 5 percent of calcium and up to 2 percentof aluminum, the remainder being iron plus its usual impurities which originate mainly from the initial materials. Commercial ferrosilicons are known which contain 1.3 to 1.5 percent of Al, 0 to 0.03 percent of Ti, 0 to 0.20 percent of Mn, 0 to 0.10 percent of Ni, 0 to 0.02 percent of Cr, 0 to 0.003 percent of S, 0 to 0.003 percent of P, 0 to 0.002 percent of Cu. Preferably, the alloy contains to percent of silicon, 0.3 to 0.7 percent of carbon, 2.0 to

4.0 percent of calcium, less than 1.5 percent of aluminum, while the remainder is iron. This alloy can be introduced into the cast iron by using the different procedures employed for the inoculation and peculiar to the foundry art.

Such an alloy can particularly be obtained by a process which consists in adding the carbon to a liquid alloy containing Si and Ca, by the addition of cast iron.

The following examples are given by way of illustrat'ion', and not by way of limitation, of the practice of this invention:

Example 1 Into a synthesis induction furnace are introduced 12 kg of an SiCa alloy (Ca 31.8 percent) and kg of industrial silicon (Si 97.7 percent); When the metal is liquid, 20 kg of small pieces of a hypereutectic cast iron titrating 5.6 percent of carbon are added. When the iron is dissolved, it is quickly poured. The product which is obtained contains:

Example 2 Ca 3.62% C 0.63

3 4 Example 3 Graphite in grain form 0.3 percent by ht In a ladle containing 607 kg of an industrial alloy in the liquid state and having the composition of: Si h percent Fe-S' IS the same that Tests I and 90.1 percent, Ca 2.8 percent, AI 1.22 percent, the 5 balance being iron and impurities, there are dissolved, Test 1 as before, 120 kg of a cast iron containing 3.14 percent Th d H d h h C and 2.3 percent Si. When the iron is dissolvedin the ls :7 a 91% f gi t e starting alloy, it is quickly poured. The product which "39? w cum: 6 m ca mm an as t e comis obtained contains:

10 Si 75.4 $1 73.8% C=047% C%=0.05

Ca 3.58 Ca=2.l1% Al%=l09 M 098% with the balance to 100 percent being iron and impuri- Example 4 ties. This alloy is elaborated by synthesis from: Inoculation tests are carried out on an identical grey h f 98 t b ht t iron with the following products prepared accordavmg a Plimy 0 percen y-welg 9 Si-Ca containing 30 percent by weight Ca and iron. ing to the prior art andin accordance with the practice of this invention: Test IV Test 1 There is used the alloy according to the invention as described in Exam le 2, the com osition of which is re- For reference purposes, there is used a 75% ferropeaed here, p p silicon of the composition: Si

A1%=1.04 L10 the balance to 100% being iron and with the balance being iron and impurities. impurities Test n At 1450 i 10 C a grey iron of mechanical type and having the following composition: There is used an alloy (not in accordance with the in- C 345 vention) which is rich in carbon and of the composi- Si 1.90 "1 Mn 0.54

S1%=74.2 p%=0 1 Ca is inoculated under the same conditions in the runner C as it is being poured. Al 1.11 For the entire series of inoculations, there are used bfifng and l under the same conditions the products 1, 11, HA, 11B,- i alloy p f y Synthesis from 98 m 40 III, IV, in a quantity such that the proportions of inocu- Slhco" and cast its pp of carbon' lating ferrous alloy represents 0.3 percent of the weight of the cast iron (i.e., an addition of 0.225 percent of sil- Test 11 A l icon on the basis Si 75 percent. There is used a mixture (not in accordance with the Each of the inoculation treatments is carried out in h Whlch carbon and compnses: a ladle containing 40 i 2 kg of cast iron, and the addi- 75 percent Fe-Si (grain size 0.5 to 2 mm) 90 pertions f the diff alloys cent by weight a Graphite in grain form 10 percent humming weight of inocuam added by weight products for 40 kg of cast iron (kg) The 75 percent Fe-Si is the same as that of Test l. i 8:58 11 A 4 Test 11 B 11 B 8.30 11] 0.120 There 18 used a mixture (not in accordance with the w 0420 invention), which is rich in carbon and comprises:

75 percent Fe-si (g Size t0 2 P The comparison results obtained with the six prodcent by weight ucts are set out in the following table:

TABLE II Number of eutectic Tempering depth,

ce1ls per cm. mm. Tensile strength Brinell hardness Inoculant Result Variation Result Variation Result Variation Result Variation I (Fe-Si comparison) 164 12 29.1 215 1i (Fe-Si-C) 174 +10 0.1 2.9 28.6 0.5 209 6 HA (Fe-Si plus 10% graphite 210 +46 V J. 8 2. 2 27.4 1. 7 202 13 11B (Fe-Si plus 0.3% graphite). 172 +8 12.1 +0.1 28. 7 -0. 4 217 +2 in (Fe-Si-Ca) 196 +32 8 4 28.3 0.8 208 7 1V (Fe-Si-Ca-C) 241 +77 4. s 7. 2 32.6 +3. 5 106 19 Reminder: cast iron not inocuiatei... 83 18 26.8 221 On tempering test but of international type.

It will be seen that test IV, representing the practice of this invention, gives the best results.

TABLE III.RESULTS OF INOCULATION ON SPHEROIDAL GRAPHITE CAST IRON Mechanical characteristics Structure on thin elements Analysis on Afpgearance of 5 mm., percent elements, percent t c Inoeulating product graphite E.L. R percent Carbides Ferrite C Si Mg l. ferrosilicon low C and low Ca Sphcroidal 36.1 59.2 14.6 45 45 3.6 2.69 0 042/0044 lli. l'errosilicon low C and with Ca do 31. 51. 0 17.5 35 65 3.6 2. 7l 0. 042/0. 044 IV, Fc-Si-CaC according to invention .(lo 31. El 50. 5 22. 2 5 65 3. 6 2 67 0. 042/0. 044

No'rE.)Characteristics in respect of a bar machined from a solid piece:

E.L.=e1astic limit (kg/mm?) R=tensile strength (kg/mini). E, percent=elongation percent.

The variation is different from that which it would have been possible to allow for when the effects of the carbon and calcium are added separately. In particular, the carbon and the calcium by themselves lead to a reduction in the tensile strength, whereas their presence together in the alloy results in an improvement in this characteristic.

Example 5 The products of tests l, II and IV of Example 4 are used this time for inoculating, for comparison purposes, a spheroidal graphite cast iron containing C 3.9 percent and Si 1.3 percent. It is known that the introduction of graphite, as in the tests HA and "B of. the preceding example, is not recommended with this type of cast iron. After nodulization treatment with a magnesium alloy, the spheroidal graphite iron is inoculated, for comparison purposes, with the three products I, II and IV, all three being used in the amount of inoculation temperature: 1460 5 C pouring temperature of the elements: 1420 5 C The compared results are set out in Table III.

The data confirms that there is a considerable gain as regards the elongation and a very substantial decrease in the percentage of carbides in the cast iron treated by the alloy according to the invention.

2. An alloy as claimed in claim 1 in which the silicon is present in an amount within the range of and percent, the carbon is present in an amount within the range of 0.3 and 0.7 percent, the calcium is present in an amount within the range of 2 and 4 percent and the aluminum is below 1.5 percent by weight.

3. The process for the preparation of the alloy of claim 1 comprising adding cast iron to a liquid bath containing silicon and calcium.

4. In the metallurgy of grey and spheroidal graphite cast irons, the step of inoculating the cast iron with an alloy of claim 1. 

2. An alloy as claimed in claim 1 in which the silicon is present in an amount within the range of 70 and 80 percent, the carbon is present in an amount within the range of 0.3 and 0.7 percent, the calcium is present in an amount within the range of 2 and 4 percent and the aluminum is below 1.5 percent by weight.
 3. The process for the preparation of the alloy of claim 1 comprising adding cast iron to a liquid bath containing silicon and calcium.
 4. In the metallurgy of grey and spheroidal graphite cast irons, the step of inoculating the cast iron with an alloy of claim
 1. 